The correct answer is the letter C: an insulated body covering, such as fur or feathers
Endotherms mainly use internally generated heat in order to maintain body temperature. This will cause their body temperature tends to stay steady regardless of the environment. On the other hand, ectotherms depend mainly on external heat sources and their body temperature changes with the temperature of the environment.
Examples of endotherms are birds and mammals
Examples of ectotherms are fishes, amphibians, reptiles, and invertebrates.
